Field of the Invention
The present invention relates to a solid-state image sensor and a camera.
Description of the Related Art
Japanese Patent Laid-Open No. 2010-245567 discloses a CMOS area sensor including a photodiode unit and a transfer MOS transistor unit. The photodiode unit is formed by a surface p-type impurity semiconductor region, an n-type impurity semiconductor region (charge accumulation region) arranged below the surface p-type impurity semiconductor region, and a p-type well arranged at least below the n-type impurity semiconductor region. The p-type well is formed by stacking a plurality of p-type impurity semiconductor regions. The p-type well is arranged so as to expand to, in addition to a region below the n-type impurity semiconductor region (charge accumulation region), a region below a transfer MOS transistor and a floating diffusion.
Generally speaking, in a solid-state image sensor, the gate length of a transfer transistor and the distance between the charge accumulation region and the floating diffusion become smaller along with a reduction in a pixel size. If the distance between the charge accumulation region and the floating diffusion becomes smaller, charges are likely to leak from the charge accumulation region to the floating diffusion. This may bring about, for example, a drop in the number of saturated charges.